1. Field of the Invention
The present invention relates to a method used in a communication device in a wireless communication system, and more particularly, to a method of radio network temporary identifier allocation in a wireless communication system.
2. Description of the Prior Art
3GPP in Release 12 proposes dual connectivity for increasing user's throughput. Dual connectivity to at least two cells may be served by different evolved NodeBs (eNB), linked with non-ideal backhaul, e.g., there may be an eNB in charge of a cluster of cells. Therefore, a user equipment (UE) may be served by multiple eNBs when it is in dual connectivity mode.
The applicant notice a problem associated to C-RNTI allocation in dual connectivity. In carrier aggregation, the C-RNTI allocation is done by a PCell and a UE is configured a C-RNTI for uplink grant or downlink assignment. In an example, the UE is connected to an eNB1 with a C-RNTI. The eNB1 may configure the UE to connect to an eNB2 to enable dual connectivity. However, the C-RNTI in the eNB2 has been assigned to another UE for data transmission and reception. When the eNB2 schedules data transmission on PDCCH with the C-RNTI, the UE and the other UE transmits data using same frequency resources in a same subframe since both UEs thinks they are scheduled by the eNB2 for uplink data transmission. Both data transmissions may fail because the eNB2 cannot receive them due to C-RNTI collision. Even the eNB2 can receive the data transmission from the UE, the eNB2 may think the data transmission is from the other UE and deciphers the data with the other UE's key but the eNB2 cannot receive the data correctly due to using a wrong key to decipher. A similar problem also occurs in downlink communication. The UE may receive the other UE's data transmitted by the eNB2 because a same C-RNTI used in the UE and the other UE.